Prior known sample collectors are exemplified by the following patents. U.S. Pat. No. Re. 29,087 discloses a particulate material sampling device wherein a hollowprobe is lowered into a grain sample, whereupon a vacuum pump causes grain to flow into a hole in the probe and through a hose into a sample container. Such arrangements provide no means to purge the walls of the probe or hose between samples. Also, such arrangements include an airflow filter which allows the smallest sample particles to pass through the filter, into the vacuum pump. Thus, a non-representative sample is obtained, especially when the intent of the sampler is to determine particle size distribution. Such particle carry-over into the pump may be detrimental to the pump.
U.S. Pat. No. 3,869,921 is exemplary of liquid sampling wherein an intake chamber is first immersed in a mass of liquid to be sampled. A pneumatic timer then cyclically operates to initiate a sampling internal by virtue of a low-pressure circuit. Operation of this timer controls a high-pressure circuit which is operative to pressurize the intake chamber and thereby force a liquid sample from this chamber to a sample container. Here again, no attempt is made to avoid contamination of a sample by a prior sample and this arrangement is not suitable for use with particulate material.
U.S. Pat. No. 3,782,200 samples flowing particulate material by means of a collecting tube having an opening in a wall thereof facing the flow path to be sampled. A piston moves in the collecting tube. One direction of piston movement evacuates the tube's particulate material to a position downstream of the tube, while subsequent movement of the piston, in the opposite direction, causes fresh material now collected in the tube to be dispensed to a sampling area. This arrangement is exemplary of sampling schemes requiring mechanical movement of a sample device, with attendant wear and contamination which are particularly associated with fine powders. In this arrangement the mechanical handling, and the energy expended in moving the sample may alter the sample's characteristics.